![]() Most other components of coffee have a boiling point that is much higher and would be solids at room temperature. The coffee is hot (or at least warm), relatively close to water’s boiling point of $100~\mathrm$ so the vapour pressure of water will be comparatively large. The key quantity you want to be looking at is vapour pressure. Thus, even assuming approximately equal distribution in the gas phase, there should still be a lot more water than anything else. It should quickly be mentioned that water is the primary component of coffee by far, hands down. it finds a surface that it feels comfortable ‘settling’ on.the part that enters the gas phase moves until.part of that solution enters the gas phase.Jan had a great point that these concepts are the foundation of the incredibly important process of distillation. No coffee molecules condense, because none were in the gas phase to begin with (essentially). So when the gaseous water molecules encounter cooler surfaces, they will transfer some kinetic energy to the surface and transition from energetic gas state to lower-energy liquid state. But water has a high vapor pressure, it is easily evaporated. There is essentially no vapor pressure, they are too bound by their IMFs to pop out and become gas (at temperatures a human usually encounters anyway). Think about the coffee residue in your pot, or the grounds - do they evaporate? Essentially no. The vapor pressure of water, despite being low relative to many organic liquids, is far higher than the vapor pressure of the molecules from coffee. This water vapor exerts a pressure based on how many molecules there are (and depending on kinetic energy / temperature), and we call this pressure from the gas above the coffee the "vapor pressure of the solution". There is much more water-gas above the solution than coffee-molecule-gas. So those water molecules that pop out are far from their neighbors, so they constitute what we call a gas or vapor. Also, the coffee solute's greater weights will make them harder to bring up to speed (though as a general rule of thumb IMFs like H-bonds actually play a more significant role than mass). As Jan said, there are many more water molecules that coffee solute molecules. Despite water being held together by the strong hydrogen bonding intermolecular force, water molecules will be first and most to gain enough energy to pop out of the liquid solution. The molecules move faster, and some at the surface break free of their attractions to their neighbors. When you heat the solution with thermal energy, when we zoom in to the molecular scale we see this energy us actually kinetic. I would expect most have dipole-dipole intermolecular forces, and (minor) hydrogen bonding may be present for some. The "coffee molecules", probably mostly alkaloids like caffeine, have larger and heavier structures than water molecules. ![]()
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